In this code, $this->environment is the current environment (i.e. dev).
In this case you have changed the location of the cache directory to
var/{environment}/cache.

Caution

You should keep the cache directory different for each environment,
otherwise some unexpected behavior may happen. Each environment generates
its own cached configuration files, and so each needs its own directory to
store those cache files.

If you need to rename or move your web directory, the only thing you
need to guarantee is that the path to the var directory is still correct
in your app.php and app_dev.php front controllers. If you simply
renamed the directory, you're fine. But if you moved it in some way, you
may need to modify these paths inside those files:

require_once__DIR__.'/../path/to/app/autoload.php';

You also need to change the extra.symfony-web-dir option in the
composer.json file:

Some shared hosts have a public_html web directory root. Renaming
your web directory from web to public_html is one way to make
your Symfony project work on your shared host. Another way is to deploy
your application to a directory outside of your web root, delete your
public_html directory, and then replace it with a symbolic link to
the web in your project.

Note

If you use the AsseticBundle, you need to configure the read_from option
to point to the correct web directory:

This modification can be of interest if you are working in a virtual environment
and cannot use NFS - for example, if you're running a Symfony application using
Vagrant/VirtualBox in a guest operating system.